1. Field of Invention
The invention relates to a planetary gear set for use in a transmission apparatus, such as an automatic transmission and the like, and, more particularly, to a carrier structure of a planetary gear set of a Ravigneaux type, a double-pinion type, or the like, having pairs of pinion gears that mesh with each other.
2. Description of Related Art
In typical transmission apparatuses, such as automatic transmissions and the like, a planetary gear set that forms a speed change mechanism is disposed around an input shaft of the transmission apparatus, an output shaft thereof, or an intermediate shaft connected to the input shaft and the output shaft, or around an axis of these shafts if the shafts are coaxially disposed. Friction members of clutches, brakes and the like for controlling the engagement and disengagement of a sun gear, a carrier and a ring gear provided as speed-changing elements with respect to an input or output member or a case are less, subject to constraints in a mount position. Therefore, the friction members are disposed between or around the planetary gear set due to an apparatus layout relationship. The brake friction members, in particular, are often disposed at an outer periphery of the planetary gear set because an outer peripheral side thereof is supported to the case of the transmission apparatus.
An inside diameter of the sun gear as a component element of the planetary gear set disposed around the aforementioned shaft, whose shaft diameter is determined in accordance with a transfer torque capacity, is restricted by the outside diameter of the shaft due to the aforementioned placement relationship. Therefore, if the apparatus is designed for higher torque, the inside diameter of the sun gear is increased, and therefore, the outside diameter of the entire planetary gear set correspondingly increases. Therefore, if friction members of friction engagement elements are disposed at an outer periphery of the planetary gear set, the outside diameter of the mechanism including the friction members becomes even greater. As a result, the placement becomes very difficult in apparatuses whose outside diameter dimensions are restricted, such as automatic transmissions installed in vehicles.
In a high torque-transferring planetary gear set, it is advantageous to increase the number of pinions in order to reduce the torque load on each pinion from the viewpoint of securing durability. However, as the number of pinions is increased, it becomes more difficult to provide a rigid carrier that supports the pinions. Obtaining a rigid carrier is even more difficult because the carrier, supporting the pinions via shafts, receives torsional moments caused by reaction forces based on the intermeshing. If the rigidity of the carrier is reduced due to the aforementioned circumstances, the carrier causes an improper gear mesh due to its deformation, thus giving rise to problems of reduction in durability, occurrence of gear noises, etc.
In the case of an ordinary simple planetary gear, the number of pinions is small (normally, three to five), and the support span of the carrier supporting the pinion is also short, so that it is relatively easy to provide a rigid planetary carrier against the aforementioned torsional force. However, if the number of pinions (normally, six to ten in three to five sets) is small as in the case of a double-pinion type planetary gear, the inter-gear space for inserting bridge members that bridge two opposite end walls of the carrier in the direction of an axis thereof is considerably restricted. If the axis length of the pinions is great as in the case of a Ravigneaux-type planetary gear, the axis length of the bridge members becomes great, so that it becomes even more difficult to provide a sectional area of the members that is sufficient to secure torsional rigidity.
With regard to a planetary carrier that supports pairs of pinion gears, a conventional technology that is considered effective to secure rigidity of the carrier is disclosed in Japanese Patent No. 2852816. This technology adopts a carrier structure in which a cup-shaped first support member is connected by welding in a two-story fashion to a cup-shaped second support member having an outer peripheral flange portion. A base wall of the first support member serves as a support portion for the two types of pinions, and a base portion of the second support member serves as another support portion for the short pinions. A peripheral wall of the second support member is partially cut and raised inwardly so as to form another support portion for the long pinions. A peripheral wall of the first support member is partially cut away to expose outer peripheries of the long pinions to an outer peripheral side of the carrier for the purpose of meshing with the ring gear.
The conventional-art Ravigneaux-type planetary carrier has a structure in which the two cup-shaped support members are connected and the carrier as a whole has a box shape, and therefore is considered effective to secure rigidity. However, the long pinion-supporting portion is a tongue-like portion formed by cutting up a peripheral wall portion. Therefore, due to this structure, the tongue-like portion has a cantilever structure in which the portion is supported only at an end side thereof by the flange portion Hence, it is assumed that the rigidity for the long pinion support is low, and it can be said that the above-described structure is not altogether suitable to a high-capacity planetary gear set.
Furthermore, the structure in which the long pinions are exposed by cutting out a portion of the peripheral wall of the cup-shaped member so as to secure a mesh can be adopted in a case where the pinion diameter is small. However, if this structure is adopted in a case where the pinion diameter is increased in order to secure a capacity and a durability of the planetary gear set that are suitable for a high-output and high-speed design, it becomes necessary to reduce the sun gear diameter. Thus, a suitable gear ratio setting becomes difficult. If a gear ratio setting is made so as to avoid a reduction of the sun gear diameter, the outside diameter of the carrier becomes great, so that the entire size of the planetary gear set becomes large. Thus, weight and size reductions will be impeded.
The invention thus provides a planetary gear set that makes it possible to dispose many pinions whose outside diameter is larger relative to the sun gear diameter while providing a rigid carrier. The invention also provides a carrier structure that, in an arrangement where friction members, such as clutches, brakes, etc., are disposed at an outer peripheral side of a planetary gear set, prevents an increase in the radial dimension of the apparatus while providing transfer torque capacities of the planetary gear set and the friction members. The invention also improves the rigidity of a carrier of a planetary gear set that supports a combination of pairs of pinion gears, and to thereby provide a planetary carrier that allows an arrangement of an increased number of pinion gear pairs and improves the durability of the planetary gear.
In order to achieve the foregoing, the invention is a planetary gear set with a plurality of pinions meshing with a sun gear and a carrier that shaft-supports the pinions, wherein the carrier has an annular peripheral wall that extends entirely around outer peripheries of the plurality of pinions, wherein the annular peripheral wall has thin-wall portions formed by recesses in a radially inner side at a circumferential-direction position corresponding to a position of the pinions.
This construction makes it possible to obtain a planetary gear set in which many pinions, whose pinion diameters are great relatively to the sun gear diameter, are disposed with an annular peripheral wall sufficient to maintain a rigidity of the carrier. Furthermore, because it becomes possible to provide an arrangement of many pinions which does not degrade the rigidity of the carrier, the torque load per pinion can be reduced, and therefore, the durability of the planetary gear set can be improved.
In the foregoing construction, the annular peripheral wall has, on an outer periphery thereof, a spline for supporting a friction member in a rotation stopping fashion, and teeth of the spline are absent in the thin-wall portions, and an outside diameter at the thin-wall portions is equal to an outside diameter at the teeth of the spline.
If a friction engagement element, such as a clutch, a brake, or the like, is disposed at the outer peripheral side of the planetary gear set, the above-described construction makes it possible to adopt an arrangement in which the spline teeth for supporting the friction member of the friction engagement element and the outside diameter of a pinion outwardly touch or overlap each other. Therefore, it becomes possible to substantially avoid a diameter increase of a mechanism due to a radial-direction superposed arrangement of the planetary gear set and friction engagement elements. Therefore, under a restricted exterior dimensional condition, it becomes possible to expand the dimension of a friction member in a radially inward direction if a torque capacity of the friction engagement element is needed, and to select the increasing of the diameter of the planetary gear set including the carrier if a torque capacity of the planetary gear set is needed. Thus, the degree of freedom in setting a power transmission apparatus employing the planetary gear set.
In either one of the foregoing constructions, it is effective to adopt a construction in which the plurality of pinions are connected to other pinions that mesh with at least a ring gear.
This construction allows a size reduction of a transmission apparatus due to an arrangement in which friction engagement elements, such as clutches, brakes, etc., and the ring gear are disposed in the direction of an axis, at the outer peripheral side of the planetary gear set.
In any one of the foregoing constructions, it is possible to adopt an application in which the plurality of pinions and the other pinions are long pinions of a Ravigneaux type planetary gear set.
This construction makes it possible to effectively achieve the advantages corresponding to the foregoing constructions, with regard to Ravigneaux type planetary gear sets in which the number of pinions tends to be great.
In the foregoing construction, it is possible to adopt an application in which the long pinions are stepped pinions in which the plurality of pinions have a smaller diameter than the other pinions.
This construction further makes it easy to secure an installation space for the friction members of friction engagement elements, such as clutches, brakes, etc., disposed at the outer peripheral side of the planetary gear set.
Next, the invention is a planetary carrier which shaft-supports intermeshing gear pairs of a first pinion that meshes with only a sun gear, and a second pinion that meshes with at least a ring gear, wherein two end portions of the carrier that shaft-support one end and another end of each pinion are connected by a bridge portion that extends in a direction of an axis, the planetary carrier being characterized in that the bridge portion has a column wall portion that fills a space between a first pinion and a second pinion of adjacent gear pairs, and a plate wall portion that extends from the column wall portion in a direction of a circumference of the carrier, and within a space between the second pinions of the adjacent gear pairs, and outwardly of the first pinion.
In this construction, the bridge portion is formed by the column wall portion and the plate wall portion by utilizing wedge-shaped spaces between first pinions and second pinions of adjacent gear pairs, and arc-shaped spaces between adjacent second pinions. Therefore, the torsional strength can be enhanced, in comparison with a conventional bridge portion formed by only a plate wall portion. Hence, it becomes possible to improve the rigidity of the entire planetary carrier. Therefore, according to this construction, an increased number of gear pairs are disposed with respect to a fixed carrier outside diameter, so as to reduce the torque transfer load per gear pair. Thus, the durability of the planetary gear set can be improved.
Furthermore, the invention is a planetary carrier which shaft-supports intermeshing gear pairs of a first pinion that meshes with only a sun gear, and a second pinion that meshes with at least a ring gear, wherein two end portions of the carrier that shaft-support one end and another end of each pinion are connected by a bridge portion that extends in a direction of an axis, the planetary gear set being characterized in that the first pinion has a smaller diameter than the second pinion, and that the bridge portion is formed by a wall that extends in a direction of a circumference of the carrier, and within a space between the second pinions of adjacent gear pairs, and outwardly of the first pinion.
In this construction, the first pinions have a smaller diameter than the second pinions, and spaces are formed outward of the first pinions with the reduced diameter, and the bridge portions are disposed in the spaces. In this manner, it is possible to construct bridge portions that are long in the circumferential-direction length, which is similar to a single-pinion construction, and that fully use the spaces between adjacent second pinions. Therefore, the torsional strength can be increased, so that the rigidity of the entire planetary carrier can be improved. Furthermore, according to this construction, the aforementioned rigidity improvement is achieved by reducing the diameter of the first pinion of each gear pair, that is, the pinion meshing with only the sun gear. Therefore, it is possible to improve the rigidity of the planetary carrier without affecting the gear ratio determined by the gear diameter of the second pinions meshed with the ring gear.
In either one of the foregoing constructions, it is effective to adopt a construction in which a supporting axis of the first pinion is positioned inward of a supporting axis of the second pinion in the direction of the circumference of the carrier.
In this construction, the first pinions are positioned relatively radially inward of the second pinions, so that the bridge portion installation spaces outward of the first pinions can be enlarged in radial directions. Therefore, the thickness of the entire bridge portions can be increased.
This construction is applicable to a case where the gear pairs are long pinions and short pinions of a Ravigneaux type planetary gear set.
This construction is able to achieve the advantages corresponding to any of the above constructions, in a planetary carrier of a Ravigneaux type planetary gear set that tends to be long in an axis-direction length because long pinions are provided as component elements.
In the foregoing construction, in particular, it is effective to adopt a construction wherein the end wall that shaft-supports an end of each pinion is a box structure wall in which an end wall that shaft-supports an end of a short pinion and an end wall that shaft-supports an end of a long pinion are connected by an axis-direction wall that continuously extends in a circumferential direction, and wherein the bridge portion connects the end wall that shaft-supports the end of the short pinion and an end wall that shaft-supports another end of each pinion.
In this construction, the end wall that cannot be formed as an end wall continuously extending in a radial direction because of the end wall supporting the long pinions and the short pinions that are different in axial length is reinforced by the box structure. Therefore, the rigidity of the bridge portion is improved, and furthermore, the rigidity of the entire planetary carrier of a Ravigneaux type planetary gear set can be improved.
The foregoing constructions are also applicable if the gear pairs are pinions of a double-pinion type planetary gear set.
This construction is able to achieve the advantages corresponding to the foregoing constructions, in the planetary carrier of a double-pinion type planetary gear set.